This invention relates to fluid circulation systems including centrifugal cleaning devices and particularly relates to drainage of cleaned fluid from such devices.
Self-powered centrifugal fluid cleaning devices are well known for cleaning lubricating fluids of solid contaminants in engines and like mechanisms. Such centrifugal cleaning devices are described for example in U.S. Pat. Nos. 4,557,831 and 4,498,898, GB-A-2160796 and EP-A-0193020.
In particular, such devices are employed with fluids in the form of liquids, and in this specification the term fluid should be construed accordingly.
It will be appreciated that notwithstanding the simplicity and efficiency with which such devices separate solids from the fluid passing therethrough, there are a number of limitations attached to their usage which have hitherto served to limit their widespread use.
A typical form of such a self-powered centrifugal cleaner is shown in part sectional elevation at 10 in FIG. 1(a), comprising a base 11, rotor 12 mounted on a substantially vertical axis 13 for rotation thereabout, a housing 14 mounted on the base and enclosing the rotor and a drain or holding sump 15 formed in the base below the rotor. A fluid inlet passage 16 is arranged to supply fluid at elevated pressure to the interior of the rotor by way of the rotation axis and a fluid drain passage 17 in the base receives fluid from the drain sump for return to a fluid reservoir. The rotor has side walls arranged to retain solid contaminants, contained in the supplied fluid, which are forced outwardly by rapid rotation of the rotor due to reaction to ejection of the supplied fluid to the drain sump by way of rotor nozzles 18, 19 in the base thereof.
In respect of use of such a cleaner in a lubrication system for an engine or a fluid operated device, the quantity of fluid which can be passed through it in a given time is limited and the fluid emerging from the rotor nozzles 18 and 19 is in a low energy state and suited only for returning by gravity flow to a system reservoir or sump.
To this end it is usual to mount the cleaner above the level of the reservoir, and indeed other parts of the circulation system whereby the static head of the fluid in the holding sump provides adequate pressure for the fluid to drain, provided of course that the gaseous atmosphere of the cleaner housing (itself a prerequisite for rotor rotation) is not at a negative pressure with respect to ambient atmospheric pressure. Usually this is achieved by having a short downwardly directed drain duct of large cross-sectional area which provide also a vent by which the housing is exposed to ambient pressure.
It has been suggested, where such a dual purpose drainage duct is not practicable, that the housing be provided with a ventilation or breather valve, such as illustrated at 14', arranged to open when the housing atmospheric pressure becomes negative to a predetermined, but finite, extent, but to ensure that the holding sump drains until the valve does open it must be sited such that the static head provides an effective drainage pressure thus further constraining its freedom of usage.
It has also been proposed to avoid draining limitations consequent upon a sub-ambient housing atmosphere pressure by exposing the housing to an above-ambient pressure, possibly from an engine crank case, although this then requires either a corresponding increase in supply pressure to maintain the pressure drop across the rotor nozzles or acceptance of a reduced rotation efficiency, or by using a suction pump driven by way of a power take off from the engine or machine being lubricated by the circulated fluid. Notwithstanding the added complexity of providing such externally powered drainage facilities which detract from the self-powered nature of the cleaner, such systems have still functioned on the basis that the cleaned and ejected fluid, whose energy has been expended in driving the rotor, is returned to the reservoir at ambient atmospheric pressure from a housing whose atmosphere is not significantly different from such pressure.
It is also known to have a fluid driven centrifugal cleaner in which the separation rotor is driven by reaction to ejection of a fluid supplied thereto at substantially constant pressure solely for that purpose whilst a fluid of indeterminate, and possibly intermittent, supply pressure is passed through, and cleaned in, the separation rotor before ejection also to join the drive fluid in the holding sump. In this case all of the fluid ejected from the rotor, that is cleaned fluid and drive fluid, is at low pressure for return to the sump and by-passes any utilisation means of the circulation system. Such a centrifugal cleaner type is described in U.S. Pat. No. 3,791,576.
U.S. Pat. No. 4,1046,315 describes a self-powered centrifugal cleaner of lubricating oil of an engine which addresses the problem of removing oil from the cleaner housing, by gravity and the limitations that places on positioning the cleaner with respect to the sump, inter alia to prevent irreversible flooding of the cleaner housing by oil from the sump. The specification describes supplying excessive oil to the centrifugal cleaner so that the surplus by-passes the cleaner centrifuge and flows through a jet pump, that includes a venturi arrangement, disposed in communication with the housing so that the flow of oil therethrough entrains oil from the housing and prevents the centrifugal cleaner from becoming inoperative due to flooding of the housing. Notwithstanding the provision of a mechanism for emptying the housing of oil as a means for removing dependency or gravitational draining to the sump, to teaching remains one of the whole centrifugal cleaning arrangement being in a by-pas circuit which diverts some of the oil circulating in the engine lubrications system from the bearing surfaces etc. for centrifugal cleaning and drains it to the sump, from which it follows that if a surplus is required in the by-pass circuit to feed the jet pump in addition to the centrifuge, then either more oil is diverted from the main engine circulation or less diverted oil is passed through the centrifugal cleaner.
A similar configuration, in which a centrifugal cleaner housing is drained by a jet pump arrangement, is described in SU-A-1409330, wherein it is taught that the jet pump creates a negative pressure within the housing for increased rotation speed. The teaching of the various examples of centrifugal cleaning arrangements referred to above indicate a general acceptance within the art that such a centrifugal fluid cleaning device has to be operated in the so-called by-pass mode in which the fluid that is diverted to flow through the cleaning arrangement bypasses the main fluid circulation and the use to which it is put.
Although centrifugal cleaners as described hereinbefore are employed primarily to separate out contaminants from lubricating oil, these are equally valid in respect of cleaning other circulated liquids fluids in liquid powered systems.
It is an object of the present invention to provide, for a liquid circulation system, a centrifugal cleaning arrangement of simple construction which is free of many of the constraints of known arrangements and permits immediate use of the cleaned fluid in the circulation system. It is also an object of the present invention to provide a liquid circulation system including such centrifugal cleaning arrangement. It is yet a further object of the present invention to provide a closed circuit liquid circulation system including such centrifugal cleaning arrangement.
According to a first aspect of the present invention, a centrifugal liquid cleaning arrangement for circulated liquid comprises a centrifugal cleaner through which a proportion of the circulated liquid is diverted, the cleaner including a rotor spun by reaction to liquid ejected therefrom through rotor nozzles and a holding sump for ejected liquid from which it is drained, and cleaner drainage assistance means comprising a primary inlet port arranged to receive circulated liquid, a diversion port arranged to divert said proportion of the liquid from the inlet port to the cleaner, an outlet port to emit said liquid and, between the diversion and outlet ports, a liquid induction arrangement including an induction port operable connected to the holding sump of the cleaner to entrain liquid from the holding sump into the non-diverted liquid flow, the cleaner drainage assistance means being characterised by pressure regulator means comprising a bypass passage extending from upstream of said Liquid induction arrangement to downstream of the induction port and including a relief valve biased to close the passage and respond to a predetermined pressure difference between inlet and outlet ports to open the passage and permit liquid to by-pass the liquid induction arrangement.
According to a second aspect of the present invention a liquid circulation system includes a liquid reservoir, a liquid circulator and a liquid cleaning arrangement as defined in the preceding paragraph.
According to a third aspect of the present invention a closed circuit liquid circulation system comprises a fluid circulator, operable to cause the liquid to circulate through the system and a centrifugal liquid cleaning arrangement as defined in the last but one paragraph, arranged to divert a proportion of the circulated liquid to the centrifugal cleaner and provide therein cleaned liquid and pass non-diverted liquid through the cleaner drainage assistance means by way of a said liquid venturi arrangement thereof and induce cleaned liquid to be entrained into the non-diverted liquid flow.
Embodiments of the invention will now be described with reference to the accompanying drawings.